The present invention relates to an improved envelope container, folder, bag and the like (hereinafter simply referred to as an envelope) and in particular to an improved expansion envelope construction.
Expansion envelopes are extensively used in many fields. One of many common applications of such envelopes is as a prepaid mailer for film processing or the like. The envelopes can be stored and sent flat prior to use and then expanded during use sufficiently to receive and securely contain the contents therein.
Heretofore, several forms of expansible envelopes have been proposed as exemplified by U.S. Pat. Nos. 67,111; 442,842; 681,,472; 2,188,730; 2,281,452; 2,460,909; 3,414,185; and 3,552,640. In the main, in each case, the prior art envelope had a single glued seam extending down the middle of the front or rear panel.
The construction of this envelope lends itself to production on standard type equipment which normally runs at a greater productive speed than expandable envelopes now being manufactured. Unlike existing expansible envelopes this unit can be produced on standard machines, some of which automatically cut and patch a window.
In view of the above, it is the principal object of the present invention to provide an improved expansible envelope. A further object is to provide a unitary integral blank from which the envelope may be produced.